My daughter is also enrolled in PM pre-school. I wasn't too happy about it as it's smack dab in the middle of her nap, and I'm not ready for her to give it up (she's 2.5 yo, and her routine was: wake up at 7:30, nap from 1-2:30, go to bed at 8 pm).
I spoke to the school director who told me that most moms in my situation would try to push up the nap time, which means making her wake up early in the morning (by 6.30) so that she'll nap by 10:30. For the first couple of months I tried very hard to get her to nap earlier by waking her up early. I thought since she has a baby sister who wakes up around 6 AM it'd work out nicely, but it was a struggle. She'd still sleep in and nap at 11.30 at the earliest, which means I usually have to wake her up for school (which I hated doing). Three months in, and all of a sudden she dropped her nap altogether and didn't seem to need it! Then a week later, she started waking up at 6 am and napping at 10:30, all on her own accord.
I guess bottom line is, kids will adapt to a new schedule, and if your child loves nap time, he'll find a way to do so!